1. Field of the Invention
The present invention relates to a pressure-bonded ball diameter detecting apparatus capable of detecting a diameter of a pressure-bonded ball bonded by a bonding apparatus and a pressure-bonded ball diameter detecting method.
2. Related Art
Wire-bonding apparatuses that connect between a pad as an electrode of a semiconductor chip and a lead as an electrode of a lead frame with a wire as a thin metal wire are widely used in a manufacturing process of semiconductor devices. Such wire-bonding apparatuses typically employ a method of sequentially bonding between a pad and a lead with a wire by forming a tip end of the wire that is inserted through a capillary and extends from a tip of the capillary into an initial ball by, for example, sparking, moving the capillary down toward the pad and pressure-bonding the initial ball to the pad using the capillary tip thereby forming a pressure-bonded ball, moving the capillary upward and then toward the lead from the pressure-bonded ball while feeding the wire from the capillary tip thereby looping the wire, moving the capillary down toward the lead and pressure-bonding the wire to the lead using the capillary tip, moving the capillary upward to cut the wire, and then moving the capillary to a position of a pad to be processed next.
In order to connect a pad and a lead in a good condition using a wire-bonding apparatus, it is necessary to make a size of a pressure-bonded ball to be a predetermined designed value. This is because a pressure-bonded ball smaller than the designed value can often result in poor bonding and a pressure-bonded ball larger than the designed value can often cause the pressure-bonded ball to protrude from the pad and to be brought into contact with an adjacent pad.
However, the size of the pressure-bonded ball can often vary during bonding due to a heating temperature of a heat block of a bonding apparatus and such. Accordingly, it is required to detect the size of the pressure-bonded ball during bonding so as to confirm that the pressure-bonded ball is bonded at a designed size. Japanese Unexamined Patent Application Publication No. H07-297220 proposes a method of detecting edges of a pressure-bonded ball based on at least three directions of lines respectively connecting a central position of a pad and points within the pad and outside the pressure-bonded ball, and calculating a position, a size, and/or a shape of the pressure-bonded ball based on the three edges of the pressure-bonded ball.
As a size of pads has increasingly become smaller along with fine-pitching of devices in recent years, there are manufactured semiconductor devices in which a diameter of a wire that extends from the pad is substantially the same as that of a pressure-bonded ball. When acquiring an image, using a camera, of a pressure-bonded ball that has been pressure-bonded to a pad of such a semiconductor chip, almost a half of a circumference of an outer shape of the pressure-bonded ball is hidden under the wire that extends from the pressure-bonded ball, and it is not possible to detect its edge by image processing.
Therefore, in bonding for fine-pitch semiconductor chips in which the diameter of the pressure-bonded ball is substantially the same as that of the wire, the method of calculating the central position and the size of the pressure-bonded ball based on the central position of the pad and the three edges of the pressure-bonded ball as proposed by Japanese Unexamined Patent Application Publication No. H07-297220 poses a problem that it is often not possible to detect the coordinates of the edges depending on a position of the pad and a position of the pressure-bonded ball as the intersection point of an X axis and a Y axis that respectively passing the center of the pad and the edges of the pressure-bonded ball are covered with the wire, and thus the size and shape of the pressure-bonded ball is often difficult to detected.